In radio communication systems such as systems based on WCDMA (Wideband Code Division Multiple Access), LTE (Long Term Evolution), and LTE-A (LTE-Advanced), which are developed by 3GPP (Third Generation Partnership Project), and Wireless LAN and WiMAX (Worldwide Interoperability for Microwave Access), which are developed by IEEE (The Institute of Electrical and Electronics engineers), a base station (cell, transmit station, transmitting device, eNodeB) and a terminal (mobile terminal, receive station, mobile station device, receiving device, UE (User Equipment)) each include a plurality of transmit/receive antennas, and employ MIMO (Multi Input Multi Output) techniques to spatially multiplex data signals to realize high-speed data communication.
In these radio communication systems, it is necessary for a base station to perform various types of control on a terminal in order to realize data communication between the base station and the terminal. To this end, a base station notifies a terminal of control information using certain resources to perform data communication in the downlink and uplink. For example, a base station notifies a terminal of information on resource allocation, information on the modulation and coding scheme of data signals, spatial multiplexing order information of data signals, transmit power control information, and so forth to realize data communication. Transmission of such control information may be implemented using the method described in NPL 1.
Various methods may be used as communication methods based on MIMO techniques in the downlink, examples of which include a multi-user MIMO scheme in which the same resources are allocated to different terminals, and a CoMP (Cooperative Multipoint, Coordinated Multipoint) scheme in which a plurality of base stations coordinate with each other to perform data communication.
FIG. 34 is a diagram illustrating an example of implementation of a multi-user MIMO scheme. In FIG. 34, a base station 3401 performs data communication with a terminal 3402 via a downlink 3404, and performs data communication with a terminal 3403 via a downlink 3405. In this case, the terminal 3402 and the terminal 3403 perform multi-user MIMO-based data communication. The downlink 3404 and the downlink 3405 use the same resources. The resources include resources in the frequency domain and the time domain. Further, the base station 3401 performs beam control for each of the downlink 3404 and the downlink 3405 using a precoding technique or the like to mutually maintain orthogonality or reduce co-channel interference. Accordingly, the base station 3401 can realize data communication with the terminal 3402 and the terminal 3403 using the same resources.
FIG. 35 is a diagram illustrating an example of implementation of a downlink CoMP scheme. In FIG. 35, the establishment of a radio communication system having a heterogeneous network configuration using a broad-coverage macro base station 3501 and an RRH (Remote Radio Head) 3502 having a narrower coverage than the macro base station 3501 is illustrated. Consideration is now given to a configuration in which the coverage of the macro base station 3501 includes part or all of the coverage of the RRH 3502. In the example illustrated in FIG. 35, the macro base station 3501 and the RRH 3502 establish a heterogeneous network configuration, and coordinate with each other to perform data communication with a terminal 3504 via a downlink 3505 and a downlink 3506, respectively. The macro base station 3501 is connected to the RRH 3502 via a line 3503, and can transmit and receive a control signal and a data signal to and from the RRH 3502. The line 3503 may be implemented using a wired line such as a fiber optic line or a wireless line that is based on relay technology. In this case, the macro base station 3501 and the RRH 3502 use frequencies (resources) some or all of which are identical, thereby improving the total spectral efficiency (transmission capacity) within the area of the coverage established by the macro base station 3501.
The terminal 3504 can perform single-cell communication with the base station 3501 or the RRH 3502 while located near the base station 3501 or the RRH 3502. While located near the edge (cell edge) of the coverage established by the RRH 3502, the terminal 3504 needs to take measures against co-channel interference from the macro base station 3501. There is under study a method for reducing or suppressing interference with the terminal 3504 in the cell-edge area using a CoMP scheme as multi-cell communication (coordinated communication) between the macro base station 3501 and the RRH 3502. In the CoMP scheme, the macro base station 3501 and the RRH 3502 coordinate with each other. The method described in NPL 2 is being studied as the CoMP scheme, by way of example.
FIG. 36 is a diagram illustrating an example of implementation of an uplink CoMP scheme. In FIG. 36, the establishment of a radio communication system having a heterogeneous network configuration using a broad-coverage macro base station 3601 and an RRH (Remote Radio Head) 3602 having a narrower coverage than that macro base station 3601 is illustrated. Consideration is now given to a configuration in which the coverage of the macro base station 3601 includes part or all of the coverage of the RRH 3602. In the example illustrated in FIG. 36, the macro base station 3601 and the RRH 3602 establish a heterogeneous network configuration, and coordinate with each other to perform data communication with a terminal 3604 via an uplink 3605 and an uplink 3606, respectively. The macro base station 3601 is connected to the RRH 3602 via a line 3603, and can transmit and receive a reception signal, a control signal, and a data signal to and from the RRH 3602. The line 3603 may be implemented using a wired line such as a fiber optic line or a wireless line that is based on relay technology. In this case, the macro base station 3601 and the RRH 3602 use frequencies (resources) some or all of which are identical, thereby improving the total spectral efficiency (transmission capacity) within the area of the coverage established by the macro base station 3601.
The terminal 3604 can perform single-cell communication with the base station 3601 or the RRH 3602 while located near the base station 3601 or the RRH 3602. In this case, while the terminal 3604 is located near the base station 3601, the base station 3601 receives and demodulates a signal received via the uplink 3605. While the terminal 3604 is located near the RRH 3602, the RRH 3602 receives and demodulates a signal received via the uplink 3606. In addition, while the terminal 3604 is located near the edge (cell edge) of the coverage established by the RRH 3602 or near a midpoint between the base station 3601 and the RRH 3602, the macro base station 3601 receives a signal received via the uplink 3605, and the RRH 3602 receives a signal received via the uplink 3606. Then, the macro base station 3601 and the RRH 3602 transmit and receive these signals, which have been received from the terminal 3604, to and from each other via the line 3603, combine the signals received from the terminal 3604, and demodulate a composite signal. Through these processing operations, improvements in the performance of data communication are expected. This is a method called Joint Reception, which enables improvements in the performance of data communication in the cell-edge area or an area near a midpoint between the macro base station 3601 and the RRH 3602 using a CoMP scheme in which the macro base station 3601 and the RRH 3602 coordinate with each other for uplink multi-cell (multipoint) communication (also called coordinated communication).